bpf: add Setter interface
bpf: add Setter interface

This interface can be implemented by types which are capable of
attaching compiled BPF filters to themselves, such as
x/net/ipv{4,6}.PacketConn.

Fixes golang/go#19912

Change-Id: I4674c3e312c173d5a7a3beb3cd53704f8c08e29b
Reviewed-on: https://go-review.googlesource.com/44972
Run-TryBot: Matt Layher <76528ff2e917253aa2211f68e4ca60b5b846dcf5@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Mikio Hara <e2f4d2eec1d9a1f781345cdd7260d7d52e6468ae@gmail.com>

golang/net